Far-field input in an audio system refers to an audio signal originating a far distance from the microphone(s). Far-field input may be from a person in a large room, a musician in a large hall, or a crowd in a stadium. Far-field input is contrasted by near-field input, which is an audio signal originating near the microphone(s). An example near-field input is a talker speaking into a cellular phone during a telephone call. Processing audio signals in the far field present additional challenges because the strength of an audio signal decays proportional to the distance of the source from the microphone. The farther a person is from a microphone, the quieter the person's voice is when it reaches the microphone. Furthermore, the presence of noise sources near the desired source can interfere with the person's voice. For example, a radio playing in the room that a person is talking makes the person difficult to hear. When the person is close to the microphone, such as in near-field processing, the person's voice is higher in amplitude than the radio. When the person is far from the microphone, such as in far-field processing, the person's voice is the same or lower in amplitude than the radio. Thus, the person's voice is more difficult to distinguish from the radio in far-field processing.
One use for far-field technology is in smart home devices. A smart home device is an electronic device configured to receive user speech input, process the speech input, and take an action based on the speech input. An example smart home device in a room is shown in FIG. 1. A living room 100 may include a smart home device 104. The smart home device 104 may include a microphone, a speaker, and electronic components for receiving speech input. Individuals 102A and 102B may be in the room and communicating with each other or speaking to the smart home device 104. Individuals 102A and 102B may be moving around the room, moving their heads, putting their hands over their face, or taking other actions that change how the smart home device 104 receives their voices. Also in the living room 100 may be sources of noise, audio signals that are not intended to activate the smart home device 104 or that interfere with the smart home device 104's reception of speech from individuals 102A and 102B. Some sources of noise include a television 110A and a radio 110B. Other sources of noise not illustrated may include washing machines, dish washers, sinks, vacuums, etc.
The smart home device 104 may incorrectly process voice commands because of the noise sources. Speech from the individuals 102A and 102B may not be recognizable by the smart home device 104 because the amplitude of noise drowns out the individual's speech. Additionally, speech from a noise source, such as television 110A, may be incorrectly recognized as a speech command. For example, a commercial on the television 110A may encourage a user to “buy product X” and the smart home device 104 may process the speech and automatically order product X. Additionally, speech from the individuals 102A and 102B may be incorrectly processed. For example, user speech for “buy backpacks” may be incorrectly recognized as “buy batteries” due to interference from the noise sources.
Shortcomings mentioned here are only representative and are included simply to highlight that a need exists for improved electrical components, particularly for audio processing employed in consumer-level devices, such as audio processing for far-field sounds in smart home devices. Embodiments described herein address certain shortcomings but not necessarily each and every one described here or known in the art. Furthermore, embodiments described herein may present other benefits than, and be used in other applications than, those of the shortcomings described above. For example, similar shortcomings may be encountered in other audio devices, such as mobile phones, and embodiments described herein may be used in mobile phones to solve such similar shortcomings as well as other shortcomings.